The study of extremophilic phages may reveal new phage families as well as different mechanisms of infection, propagation and lysis to those found in phages from temperate environments. We describe a novel siphovirus, GVE3, which infects the thermophile Geobacillus thermoglucosidasius. The genome size is 141,298 bp (G+C 29.6%), making it the largest Geobacillus spp-infecting phage known. GVE3 appears to be most closely related to the recently described Bacillus anthracis phage vB_BanS_Tsamsa, rather than Geobacillus-infecting phages described thus far. Tetranucleotide usage deviation analysis supports this relationship, showing that the GVE3 genome sequence correlates best with B. anthracis and Bacillus cereus genome sequences, rather than Geobacillus spp genome sequences.