We report the observation of a cubic phase consistent with the double gyroid structure in strongly Segregated diblock copolymers of PS-b-PDMS over a volume fraction (phi(PDMS)) range of similar to 0.39 to 0.45. The samples have respective molecular weights of 127 kg/mol and 73 kg/mol and degree of segregation N chi equal to 187 and 106, respectively, at annealing temperature of 130 degrees C. It is important to highlight that two out of the total four samples investigated, exhibited hexagonally close packed cylindrical domains of PDMS and alternating lamellae at phi(PDMS) = 0.39 and 0.45, respectively, indicating the possible narrow range of the DG morphology for the specific diblock copolymers. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2419-2427, 2009