On the size of minimal unsatisfiable formulas

An unsatisfiable formula is called minimal if it becomes satisfiable whenever any of its clauses are removed. We construct minimal unsatisfiable $k$-SAT formulas with $\Omega(n^k)$ clauses for $k \geq 3$, thereby negatively answering a question of Rosenfeld. This should be compared to the result of Lov\'asz which asserts that a critically 3-chromatic $k$-uniform hypergraph can have at most $\binom{n}{k-1}$ edges.