We demonstrate experimentally the increase of optical-to-terahertz conversion efficiency for GaAs-based photoconductive terahertz emitters. This increase is achieved by preventing device breakdown through series resistors, which act as a current limiter. Pulsed photoexcitation and potential current fluctuations result in heat dissipation leading to local heating, which further increases the current and may lead to device breakdown. We manage to increase the maximum bias field before device breakdown by a factor of 3 under illuminated conditions. For a laser system with 250-kHz repetition rate, the terahertz emission amplitude increases linearly with applied bias field up to 120 kV/cm bias field, which results in 3 times higher signal as compared to the standard device. Furthermore, we have also achieved this expanded breakdown prevention at 78-MHz repetition rate, where an integrated on-chip resistance leads to an enhancement of the terahertz field amplitude by 70%. This simple technique can increase the performance of almost all photoconductive terahertz emitters by using appropriate resistances according to the emitter capacitance and laser repetition rate.