The paper deals with the problem of Automatic Generation of Test Sequences for digital circuits. Genetic Algorithms have been successfully proposed to solve this industrially critical problem; however, they have some drawbacks, e.g., they are often unable to detect some hard to test faults, and require a careful tuning of the algorithm parameters. In this paper, we describe a new parallel version of an existing GA-based ATPG, which exploits competing sub-populations to overcome these problems. The new approach has been implemented in the PVM environment and has been evaluated on a workstation network using some of the standard benchmark circuits. The results show that it is able to significantly improve the results quality (by testing some ...