An LOCOS film is formed on an Si substrate, a gate oxide film and a gate electrode are formed thereon, and source/drain impurities are ion implanted into the Si substrate using the gate electrode as a mask. Then, a BPSG film is formed at a film density of 1.8 g/cm.sup.3 or more. A recessed part is formed in the BPSG film by the first photolithographic process with an etching depth of 20% or more but under 100% of the thickness of the BPSG film. Thereafter, the BPSG film is fluidized by reflow treatment to shape a part which is to be a contact hole into a funnel with an "upwards convex" curvature. Finally, the part formed into the funnel is etched to make a contact hole. As a result, wiring disconnection within the contact hole can be prevented, the diffusion depth controllability for the source/drain impurities can be improved, and the fall in the impurity density in the source/drain surface can be prevented.