We have simultaneously measured the friction and triboelectrification between two adhering SAM-coated molecularly smooth dissimilar metal surfaces using a modified surface forces apparatus. As the pressure is increased, triboelectrification increases drastically with large fluctuations about the mean. When the surfaces are in static contact, none of these effects is observed. Triboelectrification strongly depends on the friction type and force, sliding distance, contact area and sliding history. We also show that both SAMs and metal substrates contribute to the charge transfer mechanism.