A new method is proposed for the determination of the potential of zero charge of gold electrodes modified with thiol monolayers. It makes use of the immersion technique, in combination with a vapor deposition protocol to build the thiol monolayers. As compared to previous methods, the present approach provides more accurate results, particularly in the case of long-chain alkanethiol monolayers, and it is applicable to any monolayer irrespective of its degree of hydrophilicity. Results are presented for a series of 12 alkanethiol monolayers and for 11-mercaptoundecanol and 11-mercaptoundecanoic acid monolayers. Good agreement is found between the variation of the potential of zero charge along the alkanethiol series with the corresponding change of the surface work function. The potential of zero charge of the 11-mercaptoundecanoic acid monolayer is shown to depend on the extent of dissociation of the acid, thus opening the possibility of applying this type of measurements to the study of surface ionization processes.