Relating to semiconductor devices

A method of fabricating a semiconductor device with Shallow Trench Isolation (STI), said method comprising performing the following steps in the following order:

• providing a substrate comprising first and second gate regions separated by a trench formed in said substrate, wherein said trench is filled with an STI material;
• depositing a sacrificial polysilicon layer covering and in direct contact with the STI material;
• growing a thick oxide layer directly on said substrate in said first and second gate regions,
• whilst growing said thick oxide layer, oxidizing said sacrificial polysilicon layer to form an oxidized sacrificial polysilicon layer;
• removing said thick oxide layer from said first gate region to expose said substrate in said first region while leaving said thick oxide layer in said second gate region, wherein said step of removing said thick oxide layer also comprises removing said oxidized sacrificial polysilicon layer so as to at least partly expose said STI material.