The optimization of the development conditions in a lithography process is crucial for the overall lithographic performance while the study of the development step provides useful information regarding the properties of the lithographic material. In this work, high resolution e-beam resists are studied through in-situ monitoring of resist thickness evolution during the development step. In-situ monitoring of the resist thickness is conducted through fitting of the spectroscopic reflectance of resist films coated on dielectric layers on Si wafers and by using light at wavelengths that do not modify the lithographic properties of the resist film. The methodology was applied in the case of two selected commercially available high resolution e-beam resists and the dissolution process was monitored in depth. The recorded results prove that in-situ dissolution monitoring is a powerful tool for the generation of experimentally based development models for the lithographic materials employed in high resolution lithography. These dissolution rate (DR) values could be correlated with energy deposition profiles due to e-beam exposure and used as input in e-beam lithography (EBL) simulation tools in order to improve the accuracy of the simulation and decrease the number of actual test exposures for process optimization.