A method for forming a mask pattern using a multi-layer photoresist film process is disclosed. The processing is simplified from known processes by using a silylated photoresist film. A first photoresist layer is formed on substrate and part of the surface of the photoresist layer is silylated to thereby form a silylation layer. Then, a second photoresist layer is formed on the silylation layer, which is then exposed through the photo mask having a predetermined pattern. A second photoresist pattern is then formed after development. Then, a silylation layer pattern is formed by etching-back the silylation layer using the second photoresist pattern as an etching mask. The silylation pattern is then oxidized, and the first photoresist layer is etched using the oxidized silylation pattern, thereby forming a first photoresist pattern. A resolution increasing effect can be maintained using the two layer photoresist film structure without the need for an intermediate oxide film. Thus, the process is simplified and less undesired polymers are generated.