The invention relates to a device for producing single crystals, for example gallium-arsenide single crystals having a large diameter. The device comprises a cylindrical heating system with a bottom heating element (2), a top heating element (3) and a jacket heating element (5). The heating surfaces of the bottom and top heating elements are significantly greater than the cross-sectional area of the single crystal to be produced. The reaction chamber further comprises an insulator (6) which is configured such that a radial heat flow is suppressed and a strictly axial heat flow over the full height of the reaction chamber is ensured between the top heating element (3) and the bottom heating element (2).
