An ReRAM structure includes a dielectric layer. A first ReRAM and a second ReRAM are disposed on the dielectric layer. The second ReRAM is at one side of the first ReRAM. A trench is disposed in the dielectric layer between the first ReRAM and the second ReRAM. The first ReRAM includes a bottom electrode, a variable resistive layer and a top electrode. The variable resistive layer is between the bottom electrode and the top electrode. A width of the bottom electrode is smaller than a width of the top electrode. The width of the bottom electrode is smaller than a width of the variable resistive layer.