A polysilane having a repeating unit represented by the following general formula (LPS-I), ##STR1## wherein A is a bivalent organic group, R.sup.1 substituents may be the same or different and are selected from hydrogen atom and substituted or unsubstituted hydrocarbon group and silyl group. The polysilane is excellent in solublity in an organic solvent so that it can be formed into a film by way of a coating method, which is excellent in mechanical strength and heat resistance. The polysilane can be employed as an etching mask to be disposed under a resist in a manufacturing method of a semiconductor device. The polysilane exhibits anti-reflective effect during exposure, a large etch rate ratio in relative to a resist, and excellent dry etching resistance.