An improved model of the plasma column erosion is proposed for the understanding of the resistivity dependence of the plasma delay in a silicon surface barrier detector (SSBD). The resistivity of a SSBD has influence in the electric field strength in a depletion layer with the presence of a dielectric plasma column. The plasma delay for two SSBD’s with different resistivities was measured with 61 MeV16O ions, and the results are clearly reproduced by this model.