  Photoionization spectra of Se have been studied by step-wise resonance laser
ionization. The Rydberg series 4s$^2$4p$^3$($^4$S)np $^3$P$_{0,1,2}$ and
4s$^2$4p$^3$($^4$S)np $^5$P$_{1,2,3}$ were measured via different excitation
schemes. Using the Rydberg series 4s$^2$4p$^3$($^4$S)np $^3$P$_2$ with n=15-33,
the ionization potential of Se was determined with improved precision to
76658.15(2)$_{stat}$(4)$_{sys}$ cm$^{-1}$, which resolved the discrepancy in
previous literatures. Autoionizing (AI) spectra between the IP and two
neighboring converging limits of the Se ionic states
4s$^2$4p$^3$($^2$D$_{3/2}$) and 4s$^2$4p$^3$($^2$D$_{5/2}$) were obtained. In
total eight AI Rydberg series have been observed, measured and assigned.
