There is provided a resist underlayer film forming composition used in a lithography process for producing semiconductor devices. A method of producing a semiconductor device comprising: forming a coating film by applying a resist underlayer film forming composition containing a polymer, a crosslinker and a photoacid generator on a semiconductor substrate; forming an underlayer film by irradiating light to the coating film; and forming a photoresist by applying a photoresist composition on the underlayer film and heating the resultant layer. The polymer polymer is a polymer having a benzene ring or a hetero ring in a main chain or a side chain bonded to the main chain, and the content rate of a benzene ring in the polymer is 30 to 70% by mass. The polymer may be a polymer containing a lactone structure.