This paper presents a novel low-energy memory design technique, considering effective bitwidth of variables for application-specific systems, called VAbM technique. It targets the exploitation of both data locality and effective bitwidth of variables to reduce energy consumed by redundant bits. Under constraints of the number of memory banks, the VAbM technique use variable analysis results to perform allocating and assigning on-chip RAM into multiple memory banks, which have different size with different number of word lines and different number of bit lines tailored to each application requirements. Experimental results with several real embedded applications demonstrate significant energy reduction up to 64.8% over monolithic memory, and 18.4% over memory designed by banking technique.