CuCo5S8 thiospinel nanocrystals were synthesized by a modified colloidal method, and then it was used as an interfacial layer in the Au/CuCo5S8/p-Si heterojunction device to characterize the dielectric performance of the CuCo5S8 thiospinel. X-ray diffractometer (XRD) was performed to investigate structural behaviors of the CuCo5S8, and the results confirmed the crystalline structure of the CuCo5S8. While the detailed structures of the CuCo5S8 thiospinel were investigated by transmission electron microscope (TEM), the surface morphology was obtained by scanning electron microscope (SEM). Furthermore, the composition of the CuCo5S8 structures was studied and confirmed by the energy dispersive X-ray (EDX). The CuCo5S8 thiospinel were deposited between the Au and p-Si to obtain Au/CuCo5S8/p-Si heterojunction. The impedance spectroscopy technique was employed to determine the voltage- and frequency-dependent dielectric properties of the Au/CuCo5S8/p-Si heterojunction. While the frequency was changed from 100 kHz to 1 MHz with 100 kHz interval, the voltage was altered from − 2.5 V to + 2.5 V. The various dielectric parameters such as complex electric permittivity (dielectric constant (ε′) and dielectric loss (ε″)), electric modulus (M′ and M″), and ac electrical conductivity (σ) were extracted from the C–V and G–V measurements and discussed in details. The results highlighted that the Au/CuCo5S8/p-Si heterojunction device has the frequency- and voltage-dependent dielectric characteristics, and can be considered as switching applications.