The invention discloses a process of a self-aligned contact hole. The process comprises a first step of forming a layer of polysilicon on a silicon substrate, and then forming a layer of silicon oxynitride; a second step of forming a photoresist pattern using a gate-level mask; then etching the silicon oxynitride and polysilicon to form a gate of a transistor; next, etching back the silicon oxynitride on the gate; subjecting the gate to rapid thermal annealing or furnace tube, thereby forming a gate silicon dioxide protective layer; a third step of depositing silicon nitride and silicon dioxide; generally etching a silicon wafer to form a gate sidewall; then etching away the silicon oxynitride on the gate sidewall and on the top of the gate; performing source and drain region implantationand forming a cobalt-silicon alloy; and a fourth step of forming an etch stop layer and a contact hole dielectric layer, performing chemical mechanical polishing, and performing contact hole etching.According to the invention, the height of the gate sidewall is higher, the gate sidewall is thicker, the gate is better protected, and the breakdown voltage between the contact hole and the gate is improved.