Problem: We evaluated mortality during 1965 to 1999 among 126,836 workers at two semiconductor facilities and one storage device facility. Method: We compared employees' cause-specific mortality rates with general population rates and examined mortality patterns by facility, duration of employment, time since first employment, and work activity. Results: Employees had lower-than-expected mortality overall (6579 observed deaths, standardized mortality ratio [SMR] = 65; 95% confidence interval [CI] = 64-67), for all cancers combined (2159 observed, SMR= 78, 95% CI = 75-81) and for other major diseases. Central nervous system cancer was associated with process equipment maintenance at one of the semiconductor facilities (10 observed, SMR = 247, 95% CI = 118-454). Prostate cancer was associated with facilities/laboratories at the storage device facility (18 observed, SMR = 198, (5% CI = 117-313). Conclusions: Further evaluation of workplace exposures or independent investigations of similar occupational groups may clarify the interpretation of associations observed in this study. Copyright © by American College of Occupational and Environmental Medicine.