A transistor device includes a semiconductor epitaxial layer structure including a channel layer and a barrier layer on the channel layer, wherein the barrier layer has a higher bandgap than the channel layer. A modified access region is provided at an upper surface of the barrier layer opposite the channel layer. The modified access region includes a material having a lower surface barrier height than the barrier layer. A source contact and a drain contact are formed on the barrier layer, and a gate contact is formed between source contact and the drain contact.

A monolithically-integrated AC switch includes a semiconductor substrate having first and second insulated-gate field effect transistors therein, which contain first and second spaced-apart and independently-controllable source terminals extending adjacent a first surface of the semiconductor substrate, yet share a common drain electrode extending adjacent a second surface of the semiconductor substrate. According to some of these embodiments of the invention, the first and second insulated-gate field effect transistors include respective first and second independently-controllable gate electrodes, which extend adjacent the first surface. The first and second insulated-gate field effect transistors may be configured as first and second vertical power MOSFETs, respectively. The semiconductor substrate may also include at least one edge termination region therein, which extends between the first and second vertical power MOSFETs.

A compound semiconductor device includes: a compound semiconductor area in which a compound semiconductor plug is embedded and formed; and an ohmic electrode provided on the compound semiconductor plug, wherein the compound semiconductor plug includes, in a side surface portion that is as an interface with the compound semiconductor area, a high concentration dopant layer containing a dopant whose concentration is higher than that of other portions.

A method for manufacturing a semiconductor device comprises forming a bottom source/drain region on a semiconductor substrate, forming a channel region extending vertically from the bottom source/drain region, growing a top source/drain region from an upper portion of the channel region, and growing a gate region from a lower portion of the channel region under the upper portion, wherein the gate region is on more than one side of the channel region.

An industrially useful p-type oxide semiconductor with an enhanced semiconductor characteristic and a method of forming the p-type oxide semiconductor is provided. By using a metal oxide (for example, iridium oxide) gas as a raw material and conducting a crystal growth on a base with a corundum structure (for example, a sapphire substrate) until a film thickness to be equal to or more than 50 nm, a p-type oxide semiconductor film with a corundum structure includes a film thickness of equal to or more than 50 nm and a surface roughness of equal to or less than 10 nm is obtained.

A semiconductor device is provided. The semiconductor device includes a substrate; an active layer disposed on the substrate; a via through the active layer; and a plurality of electrodes disposed on the active layer and into the via. Additionally, a package structure that includes the semiconductor device is also provided. The electrode is electrically connected to the substrate through the via.

A four-terminal GaN transistor and methods of manufacture, the transistor having source and drain regions and preferably two T-shaped gate electrodes, wherein a stem of one of the two T-shaped gate electrodes is more closely located to the source region than it is to a stem of the other one of the two T-shaped gate electrodes and wherein the stem of the other one of the two T-shaped gate electrodes is more closely located to the drain region than it is to the stem of said one of the two T-shaped gate electrodes. The the gate closer to the source region is a T-gate, and the proximity of the two gates is less than 500 nm from each other. The spacing between the stem of the RF gate and source region and the stem of the DC gate and drain region are preferably defined by self-aligned fabrication techniques. The four-terminal GaN transistor is capable of operation in the W-band (75 to 100 GHz).

In a semiconductor device having a heterojunction type superjunction structure, a drain portion and a source portion are electrically connected to one of a two-dimensional electron gas layer and a two-dimensional hole gas layer, and a gate portion is prevented by an insulating region from directly contacting the one of the two-dimensional election gas layer and the two-dimensional hole gas layer.

A field-effect transistor includes a source electrode, a drain electrode, a semiconductor structure including a channel provided between the source electrode and the drain electrode in a first direction. Gate main portions have a first gate main portion length in the first direction and a second gate main portion length in a second direction. Connection portions are alternatively connected to the gate main portions respectively in the second direction. Each of the connection portions has a first connection portion length in the first direction and a second connection portion length in the second direction. The first connection portion length is longer than the first gate main portion length. The second connection portion length is shorter than the second gate main portion length. An external connection section is to apply electric power to the gate electrode. A bypass electrode connects the external connection section to each of the connection portions.

A process of forming a field transistor (FET) and a FET are disclosed. The FET includes a nitride semiconductor stack on a substrate. A pair of n.sup.+-regions made of oxide semiconductor material are provided within respective recesses in the semiconductor stack. Protecting layers, each made of oxide material, cover peripheries of the n.sup.+-regions. Electrodes are provided in openings in the protecting layers to be in direct contact with the n.sup.+-regions.