The temperature gradient liquid phase epitaxy under a steady natural convection flow was introduced. The steady natural convection flow was caused by applying a horizontal temperature difference to the growth solution. The growth rate in this process was calculated using a simple model. It was found that the growth rate is directly proportional to the square root of the horizontal temperature difference and for Ga0.85Al0.15 As growth under the condition employed in the present work the growth rate is 1124 times as great as that predicted by the steady state diffusion theory and the deviation of epitaxial layer thickness is not more than 10% over the most part of area of growth layer. The experimental growth system designed for the temperature gradient liquid phase epitaxy under a steady natural convection flow was described. This system was used to grow thick Ga0.85Al0.15 As layers. The experimental result shows that the observed growth rate is directly proportional to the power 0.45 of the horizontal temperature difference and for Ga0.85Al0.15 As growth the observed growth rate is 156 times as great as that predicted by the steady state diffusion theory and is one-eighth as great as that predicted by the convection theory and at a relatively small horizontal temperature difference the deviation of epitaxial layer thickness is in agreement with the calculated value by the convection theory. The calculated growth rate is higher than the observed growth rate. That is attributed to some approximations made and some indefinite parameters used. Owing to an increase in growth rate the present work was able to grew thick Ga1-xAlx As layers at the temperature which is 135-210℃ lower than that used for the similar work.