East-West migration in Germany peaked at the beginning of the 1990s although the average wage gap between Eastern and Western Germany continues to average about 25%. We analyse the propensity to migrate using microdata from the German Socioeconomic Panel. Fitting a parametric Generalized Linear Model (GLM) yields non-linear residual behavior. This finding is not compatible with classical Marshallian theory of migration and motivates the semiparametric analysis. We estimate a Generalized Partial Linear Model (GPLM) where some components of the index of explanatory variables enter non-parametrically. We find the estimate of the non-parametric influence in concordance with a number of alternative migration theories, including the recently proposed option-value-of-waiting theory.