A device includes a semiconductor fin, a gate structure, gate spacers, and a dielectric feature. The semiconductor fin is over a substrate. The gate structure is over the semiconductor fin and includes a gate dielectric layer over the semiconductor fin and a gate metal covering the gate dielectric layer. The gate spacers are on opposite sides of the gate structure. The dielectric feature is over the substrate. The dielectric feature is in contact with the gate metal, the gate dielectric layer, and the gate spacers, and an interface between the gate metal and the dielectric feature is substantially aligned with an interface between the dielectric feature and one of the gate spacers.

A method for manufacturing a semiconductor device includes: forming a semiconductor structure on a semiconductor substrate, the semiconductor structure including first and second source/drain regions disposed on the semiconductor substrate in a first direction and spaced apart from each other in a second direction transverse to the first direction, and a plurality of channel features disposed between and connected to the first and second source/drain regions and spaced apart from one another in the first direction; forming an interfacial material layer to cover the channel features; forming a metal oxide layer on the interfacial material layer; converting a portion of the interfacial material layer into a metal silicate layer so as to form a plurality of interfacial features respectively covering the channel features, the metal silicate layer being formed between the metal oxide layer and the interfacial features; and removing the metal oxide layer and the metal silicate layer.