Semiconductor memories are highly vulnerable to adjacent double bit errors for two reasons: 1) The bombardment of strong radioactive particles such as cosmic particles on DRAM chips and data bit lines. 2) The coupling noise in recent high density DRAM chips due to the wiring capacitance between two adjacent data bit lines. In addition, byte errors which result from entire chip failures are also a source of concern. Under this situation, codes capable of correcting adjacent double bit errors and simultaneously detecting single byte errors are suitable for application in semiconductor memory systems. This paper proposes two classes of codes called Adjacent Double bit Error Correcting-Single b-bit Byte Error Detecting (ADEC-SbED) codes and Adjacent Double bit within a b-bit byte Error Correcting-Single b-bit byte Error Detecting ((ADEC)b-SbED) codes. For the practical case where byte length is 4 bits, the proposed codes require at most one extra check bit than their bounds. Furthermore, the number check bits required by the proposed (ADEC)4-S4ED code is same as that of the well known SEC-DED code for practical information bit lengths such as 64, 128, 256, etc.