film 41 it is also possible to form this second insulating film by using instead of a silicon nitride film a silicon oxide sio film a silicon oxycarbide sioc film or the like having the above described characteristic the u201c sin u201d refers to a compound of si and n the u201c sio u201d refers to a compound of si and o and the u201c sioc u201d refers to a compound of si o and c these u201c sin u201d u201c sio u201d and u201c sioc u201d will not limit the composition ratios of the compounds this applies also to the following description over the n type field effect transistor 3 and the p type substrate region 16 a third insulating film 43 that covers the transistor 3 and the region 16 and has tensile stress is formed this third insulating film 43 is formed of e g a silicon nitride film having tensile stress in this semiconductor device 1 1 b the n type substrate region 14 is covered by the second insulating film 42 having tensile stress or compressive stress lower than that of the first insulating film 41 covering the p type field effect transistor 2 therefore although the density of the first insulating film 41 is high the density of the second insulating film 42 is lower than that of the first insulating film 41 in particular the density of the second insulating film 42.