In a method for manufacturing a semiconductor pressure sensor, after a reference pressure chamber is formed inside a semiconductor substrate and a diaphragm is formed from a part of the semiconductor substrate, a heat treatment is performed to form an insulation film, an element, or the like on the semiconductor substrate. At that time, a heat treatment temperature is controlled to be lower than (−430P0+1430)° C. where P0 is an internal pressure (atm) of the reference pressure chamber at a room temperature. Accordingly, crystal defects can be prevented from being produced in the diaphragm.