A method of forming a buried plate electrode for a trench capacitor of a semiconductor memory device is provided. Trenches are formed in a semiconductor substrate and a dopant source film is formed on the sidewalls and bottom walls of the trenches. A resist is formed on the dopant source film which fills in the trenches. The resist is recessed to remain in the trenches at a level which is below the surface of the semiconductor substrate. Impurities are implanted into the semiconductor substrate using the recessed resist as a block mask. The dopant source film is etched using the recessed resist as an etching mask and the recessed resist is then removed. The implanted impurities and dopants from the dopant source film are diffused into the semiconductor substrate to form a buried plate electrode.