The electrical properties of Sip+-i-n+diodes with a hole injecting gate are studied. The gate is placed between the anode (p+) and the cathode (n+). Under appropriate conditions of both the gate location and the positive gate voltage with respect to the cathode, these devices exhibit voltage-controlled negative resistance (VCNR). A phenomenological model for the occurrence of VCNR is proposed. The model considers the interaction between twop+-i-n+diodes fabricated in the same substrate. Electrical characteristics are analysed on the basis of this model. The experimental results can be understood phenomenologically using the above model.