by anodic oxidation before forming the photoresist good adhesiveness with the photoresist was obtained further since the aluminum oxide film suppressed a leak current from the photoresist it was effective in forming a porous anodic oxide film on only the side faces in a later anodic oxidation step then the photoresist and the aluminum film were together patterned i e etched to produce gate electrodes 26 and 27 and mask films 28 and 29 in this embodiment the width of the gate electrode 27 of the n channel tft was made 7 u03bcm and the width of the gate electrode 26 of the p channel tft was made 4 gm see fig3 a then anodic oxide films 30 and 31 of 3 000 6 000 u00e5 for instance 5 000 u00e5 in thickness were formed by anodic oxidation in which a current was caused to flow through the above structure in an electrolyte the anodic oxidation can be performed by using citric acid of 3 20 or an acidic aqueous solution of oxalic acid phosphoric acid chromic acid sulfuric acid or the like and applying 10 30 v to the gate electrodes with the electric current kept constant in this embodiment anodic oxidation was performed in an oxalic acid solution.