Kinetic coefficient on a solid/liquid interface in liquid-phase epitaxial growth of GaP/GaP(I I I)B was measured by an in situ observation technique using a near-infrared microscopic interferometer under a static magnetic field of 4T. The morphological stability of the interface during the 'growth was quantitatively evaluated based on a linear perturbational approach taking account of the kinetic coefficient. The calculated value of the macrostep wavelength agreed well with the measured one. (C) 2002 Elsevier Science B.V. All rights reserved.