Cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives have been synthesized to control a position and a distance between charged head groups on gold substrates. Three molecules bearing resembling molecular structures, "gemini"-structured didodecyl dithiol (HS-gQA-SH), didodecyl disulfide (QA-SS-QA), and gemini-structured didodecyl disulfide (gQA-SS-gQA), were utilized in this study, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR).