The mass resolved electronic spectrum of cold tryptophan molecules has been obtained using a novel desorption method as a vaporization source coupled with a supersonic expansion. This desorption device is characterized by its simplicity, stability suitable for spectroscopic studies and by a very low yield of fragmentation products. The unique performance of the desorption source is demonstrated by the possibility to measure hole-burning spectra of tryptophan by resonance enhanced two-photon ionization which confirms strongly the presence of only a small number of stable conformers for this species in its ground state.