Power transistor with trench sinker for contacting the backside

A power transistor includes a first semiconductor region of a first conductivity type extending over and in contact with a second semiconductor region of the first conductivity type. Gate trenches extend into the first semiconductor region. Well regions of a second conductivity type extend over the first semiconductor region and between adjacent gate trenches. A sinker trench extends through the first semiconductor region and terminates within the second semiconductor region, and is laterally spaced from an outer one of the gate trenches with no well regions abutting sidewalls of the sinker trench. Source regions of the first conductivity type extend over the well regions. A conductive material in the sinker trench makes electrical contact with the second semiconductor region along the bottom of the sinker trench and with a drain interconnect layer extending along the top of the sinker trench.