Delocalized lipophilic cations such as tri‐ and tetra‐arylphosphonium are able to diffuse across the mitochondrial membrane, which allows them to selectively accumulate in cells with a high transmembrane potential (ΔΨm). The mitochondrial membrane potential of cancer cells and cardiomyocytes has been reported to be significantly higher than that of normal epithelial cells. This feature can be exploited for the selective accumulation of phosphonium derivatives for the purposes of molecular imaging using radionuclides. Four structurally related Ga(III)‐phosphonium salts were synthesized and fully characterized and found to be modest in toxicity toward T98G human glioblastoma cells (IC50 > 4 mM). High‐activity (100 MBq) analogs containing Ga‐67 were also synthesized and their stabilities in phosphate‐buffered saline and human serum were determined.