In one embodiment, a vertical insulated-gate field effect transistor includes a shield electrode formed in trench structure within a semiconductor material. A gate electrode is isolated from the semiconductor material using gate insulating layers. Before the shield electrode is formed, spacer layers can be used form shield insulating layers along portions of the trench structure. The shield insulating layers are thicker than the gate insulating layers. In another embodiment, the shield insulating layers have variable thickness.