In fabrication of a semiconductor device which is provided with resistances and MOS transistors on the same substrate, conduction failures of contacts and leaching of wiring metal into a silicon substrate is prevented. Firstly, an underlying structure is prepared. Then, a silicon oxide layer is formed on the underlying structure. Then, a silicon nitride layer is formed on the silicon oxide layer. Then, an inter-layer insulation layer is formed on the silicon nitride layer. Then, a contact hole is formed penetrating through a laminate of the silicon oxide layer, the silicon nitride layer and the inter-layer insulation layer. A thickness of the silicon oxide layer is a value in a range from 32 nm to 48 nm.