Electroabsorption has been measured with thin films of several (phthalocyaninato)galliums. It has been observed that the lowest energy absorption peak of most of the compounds studied is sensitive to the applied electric field. The shape of the electroabsorption spectrum is well reproduced by the second derivative of the corresponding absorption, indicating that the excited state has the character of a charge transfer state. It has been found that a clear correlation exists between the magnitude of the electromodulation and the sensitivity for the charge carrier generation. Crystal structure analysis of two compounds, hydroxygallium phthalocyanine type XI and chlorogallium phthalocyanine type II, made by Rietveld analysis, clarified that the molecules are stacked in pairs. The implication of the dimer structure is discussed.