Electrostatic ion‐cyclotron (EIC) waves have been investigated in plasmas containing K+positive ions, electrons, and SF−6negative ions. Two EIC wave modes are generally present, the K+and SF−6modes. Their frequencies increase with increasing &egr;, the percentage of negative ions, while the critical electron drift velocities for excitation of either mode decrease with increasing &egr;. The observations are discussed on the basis of available theories.