groove 30 is formed by depositing a silicon oxide film 31 and a silicon nitride film 32 consecutively over the semiconductor substrate 1 and then by dry etching the silicon nitride 32 the silicon oxide film 31 and the semiconductor substrate 1 consecutively by using a photoresist as the mask next a silicon oxide film 36 is buried in the groove 30 to form the element isolating groove 2 as shown in fig8 a and 8 b the element isolating groove 2 is formed by depositing the silicon oxide film 36 thickly over the semiconductor substrate 1 including the inside of the groove 30 by a cvd chemical vapor deposition method and then by etching back chemico mechanical polishing cmp the silicon oxide film 36 by using the silicon nitride film 32 as an etching stopper next the silicon nitride film 32 and the silicon oxide film 31 left on the surface of the active region ar are etched away after this as shown in fig9 and 10 a and 10 b the semiconductor substrate 1 of the active region ar where the drive misfets qd 1 and qd 2 and the transfer misfets qt 1 and qt 2 are formed is doped with ions of p type impurity boron to form the p type well 3 and the semiconductor substrate 1 of the active region ar where the load misfets qp 1 and qp 2 are formed is doped with ions of an.