An acetal-protected polysiloxane composition, used as a photosensitive composition and a coating composition for forming a flat film on a substrate to be processed for performing pattern reversal. A coating composition or photosensitive composition including: a polysiloxane obtained from a hydrolysis-condensation product of a hydrolyzable silane having 2 to 4 hydrolyzable groups in a molecule by protecting the condensation product's silanol groups with acetal groups, wherein in the hydrolysis-condensation product, an organic group bonded to silicon atoms through Si—C bonds exists in molar ratio of 0≤(organic group)/(Si)≤0.29 on average. Method for producing semiconductor device, including steps: forming resist film on a semiconductor substrate; exposing resist film and developing resist after exposure to obtain resist pattern; applying the coating composition onto patterned resist film to embed the polysiloxane; curing the embedded polysiloxane and then etching resist film to reverse the pattern; and processing substrate using polysiloxane film.