Thick films of hydroxyapatite (HA) were deposited on silicon single crystal wafers placed in close proximity to a plate of apatite-and wollastonite-containing glass and dipped into a simulated physiological solution at 36 °C. Amorphous calcium phosphate phase present in the glass leached into the solution, causing supersaturation of Ca 2+ and PO 3-ions. Spherical cap-like islands of calcium phosphate nucleated on Si crystals and grew in size with time. The thickness of the film grown on Si (1 1 1) in a solution having a composition similar to that of human blood plasma, and maintained at pH of 7.2, reached 7.1 lam in 336 h, compared with a thickness of 12.7 lam when the ion concentrations of the solution were doubled. HA films grown on Si (1 1 1) showed strong (1 02) texture. In contrast, hardly any HA film could be grown on Si (1 00). With increasing pH value of the solution the Ca/P ratio of the film increased. At a pH of 7.2 the as-grown and annealed (at 800 °C for 3 h in argon) films had Ca/P ratios of 1.10 and 1.72, respectively. The Vickers hardness and the adhesion strength of the film increased upon annealing. Our results suggest that the driving force for formation of apatite films arises from the lowering of free energy of the supersaturated solution by deposition of ions (Ca, P, O, H) in certain crystallographic arrangements on suitable substrates with low interface energies.