The invention relates to a semiconductor memory device, a manufacturing method thereof, and an electronic device. The method includes: a step S1: providing a semiconductor substrate, and forming gate structures on the semiconductor substrate; a step S2: forming first gap walls on side walls of the gate structures, and performing LDD injection to forming LDD areas in the semiconductor substrate at two sides of the gate structures; a step S3: removing the first gap walls to expose the gate structures; and a step S4: forming second gap walls on the side walls of the gate structures, and performing source and drain injection to form source electrodes and drain electrodes on the semiconductor substrate. The breakdown performance of the semiconductor memory device manufactured through the method can be greatly improved, and the yield of the semiconductor memory device can be also improved.