Morphologies of Si surfaces treated with aqueous solutions of hydrofluoric acid (HF) and ammonium fluoride (NH4F) have been investigated using surface infrared spectroscopy. We confirm that HF‐treated Si(111) surfaces are terminated with a monohydride (Si—H), dihydride (Si—H2), and trihydride (Si–H3), whereas NH4F‐treated Si(111) surfaces are dominantly terminated with Si—H. For Si(100), treatment in NH4F produces a surface for which the dihydride mode is enhanced compared to HF treatment, suggesting that surface Si—Si bonds on Si(100) are readily cleaved in a NH4F solution to generate a dihydride Si. The effect of varying the HF concentration on the morphology of HF‐treated Si(100) surfaces is investigated. It is demonstrated that 5% HF treatment produces Si(100) surfaces which have a larger density of surface Si—Si bonds than 50% HF or 0.5% HF treatment.