The present invention provides an additive for a photoresist composition for a resist flow process. A compound of following Formula 1 having low glass transition temperature is added to a photoresist composition containing a polymer which is not suitable for the resist flow process due to its high glass transition temperature, thus improving a flow property of the photoresist composition. As a result, the photoresist composition comprising an additive of Formula 1 can be used for the resist flow process. wherein, A, B, R and R′ are as defined in the specification of the invention.