Static Random-Access Memories (SRAMs) have flourished in the memory market relying on their speed, power consumption and compatibility with standard CMOS process technology. Conventional SRAMs are characterized by volatility, limiting their role in applications where non-volatility is essential. Non-Volatile SRAMs (NVSRAMs) represent an appealing solution, where Resistive RAM (RRAM) can act as a non-volatile element for SRAM. RRAM relies on the basic physical phenomenon of operation called resistive switching. This paper presents different NVSRAM structures, while exploring their principle of operation. Also, a comparison in terms of area, speed, power consumption and design complexity is presented for three NVSRAM memory cells implemented in a 130-nm high voltage CMOS technology from STMicroelectronics.