Vacuum thermionic emission behaviors from bare silicon and chemical vapor deposition diamond coated silicon using laser pulse heating are reported. Under vacuum and subjected to a moderate biasing voltage, the bare silicon and diamond coated silicon emitters show pulses of emission current synchronized with the excitations of nanoseconds 532 urn Nd:YAG pulsed laser. The peak emission current increased monotonically with the increased in laser pulse intensity. The Arrhenius plot of the emission current versus laser intensity follows Richardson's thermionic emission equation for the bare silicon emitter. The diamond-coated silicon emitter shows two activation energies: a value same as that of the bare silicon at low laser intensity and transit to a zero value at high laser intensity. 2009 American Vacuum Society. [DOI: 10.1116/1.3077486]