A polishing agent which has excellent storage stability and a high selective ratio between a silicon oxide and a stopper film while maintaining the silicon oxide removal. A polishing agent containing abrasive grains, an anionic polymer, an acidic compound selected from phosphoric acid compounds and organic acid compounds, and water, wherein the anionic polymer is a copolymer containing a hydrophobic monomer and an anionic monomer, an acid value of the anionic polymer is 20 to 400 mgKOH/g; a partition coefficient of the hydrophobic monomer is 0 to 4; the anionic monomer contains at least one type selected from unsaturated monocarboxylic acids and salts thereof, and when an acid compound having a highest molar concentration among the acidic compounds is defined as a first acidic compound, pKa of the first acidic compound and pH of the polishing agent satisfy a following relationship: |pKapH|1.5.

A semiconductor package may include a first semiconductor die having a first width; a second semiconductor die on the first semiconductor die, the second semiconductor die having a second width that is smaller than the first width; and a mold layer at least partially covering a side surface of the second semiconductor die, and a top surface of the first semiconductor die, wherein the first semiconductor die comprises at least one first detection pattern, the at least one first detection pattern being on the top surface of the first semiconductor die and in contact with a bottom surface of the mold layer.