Proteins, in the presence of trivalent cations, exhibit intriguing phase behavior which is contrasting compared to mono- and divalent cations. At room temperature (RT), trivalent cations induce microscopic liquid–liquid phase separation (LLPS) in which a protein-rich phase coexists with a dilute phase. The critical solution temperature related phenomena in these complex fluids are well studied; however, such studies have mostly been restricted below the denaturation temperature (TM) of the protein(s) involved. Here, we probe the phase behavior of bovine serum albumin (BSA) incubated at 70 °C (>TM) in the presence of Na+, Mg2+, La3+, Y3+, and Ho3+ ions. BSA in the presence of mono- and bivalent ions forms an intense gel phase at 70 °C; however, the trivalent salts offer remarkable thermal resistivity and retain the fluid LLPS phase. We determine the microscopic phase behavior using differential interference …