Non-topcoat (non-TC) resists, which blend hydrophobic additives into a resist polymer, have been proposed by vendors. To minimize the surface free energy, a hydrophobic additive segregates to the surface and forms a layer. The improvement of surface hydrophobicity and the suppression of resist component leaching are achieved by using this segregation layer. Segregation is an unstable physical phenomenon that is influenced by the environment. Hence, the characteristics of segregation layers must be sufficiently understood to use non-TC resists safely and have been thoroughly investigated using various analyses in this study. The results revealed the following: (1) A segregation layer comprising only the hydrophobic additive could form if the additive had low critical surface tension. However, the segregation layer differed from the coating film and exhibited a film density comparable to that of the base polymer. (2) The segregation mostly occurred during spin coating. (3) A non-TC resist should have the optimum film thickness: a thin film exhibited low hydrophobicity, whereas the additive remained in the resist bulk for a thick film. (4) There were no differences in the segregation layer in the central and outer parts of the wafer. When using a non-TC resist, it is necessary to understand the characteristics and note the usage. If it is used with sufficient understanding, it is sure that a non-TC resist can reduce the cost and increase the throughput safely.