A semiconductor device manufacturing method which sequentially forms a gate oxide film and gate electrode material over a semiconductor layer of an SOI substrate and patterns the material into gate electrodes. The method further comprises the steps of forming sidewalls made of an insulator to cover side surfaces of the gate electrode; ion-implanting into the semiconductor layer on both sides of the gate electrode to form drain/source regions; partially etching the sidewalls to expose upper parts of the side surfaces of the gate electrode; depositing a metal film to cover the tops of the drain/source regions and of the gate electrode and the exposed upper parts of the side surfaces of the gate electrode; and performing heat treatment on the SOI substrate to form silicide layers respectively in the surfaces of the gate electrode and of the drain/source regions.