Excitons play an important role in semiconductor physics, whereas their electrical characteristics have rarely been explored. Here, AC differential capacitance response spectroscopy is applied to GaN-based multi-quantum-well (MQW) laser diodes (LDs) to investigate the transition-bound excitons. The capacitance response aligns with a modified rate equation, exhibiting "negative activation energy", attributed to a sub-stable transition-bound state. Temperature dependent measurements yield binding energies of the transition-bound state consistent with weakly confined excitons in III-V quantum structures. These results confirm transition-bound excitons under continuous electrical excitation. As a comparison, the differential capacitance response of GaAs-based MQW LDs have shown that there is no "negative activation energy", which further confirms the transition-bound excitons in GaN-based MQW LDs at room temperature. In addition, simulations of GaN-based MQW LDs' capacitance response match experimental results well.