Static random access memories (SRAM) are provided. The SRAM includes a plurality of bit cells. Each bit cell includes a first inverter, a second inverter cross-coupled with the first inverter, a first pass gate transistor coupled between the first inverter and a bit line, and a second pass gate transistor coupled between the second inverter and a complementary bit line. The bit cells are divided into a plurality of top tier cells and a plurality of bottom tier cells, and each of the bottom tier cells is disposed under the individual top tier cell. The first inverter of the top tier cell is disposed on the second inverter of the corresponding bottom tier cell within a substrate, and the second inverter of the top tier cell is disposed on the first inverter of the corresponding bottom tier cell within the substrate.