EuRh2Si2 is well known to show a valence transition at a pressure of about 1 GPa from a Eu-divalent (antiferromagnetic) state to a nearly Eu-trivalent (paramagnetic) state, which was clarified using polycrystalline samples. We have succeeded in growing single crystals of EuRh2Si2 by the Bridgman method and studied their electronic properties measuring the electrical resistivity under pressure. EuRh2Si2 indicates a first-order valence transition in the pressure range from 1 to 2 GPa, distinguished by a sharp transition and a prominent hysteresis in the temperature dependence of the electrical resistivity. A critical end point in the valence transition is estimated as P-CEP similar or equal to 2.05 GPa and T-CEP similar or equal to 170 K. In the pressure range from 2 to 3 GPa, the electrical resistivity is found to exhibit a characteristic behavior for a moderately heavy-fermion compound such as EuIr2Si2. At pressures higher than 3 GPa, the resistivity reveals a normal metallic behavior in a nearly trivalent electronic state. This is the first report on the pressure evolution of the electronic states from the antiferromagnetically ordered state to the moderate heavy-fermion state and nearly trivalent state, via the first-order valence transition.