Abstract. We present a detailed bifurcation analysis of a single-mode semiconductor laser subject to phaseconjugate feedback, a system described by a delay differential equation. Codimension-one bifurcation curves of equilibria and periodic orbits and curves of certain connecting orbits are presented near the laser's locking region in the two-dimensional parameter plane of feedback strength and pump current. We identify several codimension-two bifurcations, including a double-Hopf point, Belyakov points, and a T-point bifurcation, and we show how they organize the dynamics. This study is the first example of a two-parameter bifurcation study, including bifurcations of periodic and connecting orbits, of a delay system. It was made possible by new numerical continuation tools, implemented in the package DDE-BIFTOOL, and showcases their usefulness for the study of delay systems arising in applications.Key words. semiconductor lasers, phase-conjugate feedback, delay differential equations, two-parameter continuation, heteroclinic orbits, T-point bifurcation AMS subject classifications. 37N20, 34K18, 37G10, 37G20PII. S11111111024165751. Introduction. The majority of lasers in application today are semiconductor lasers. They can be found, for example, in CD-players, laser printers, and optical communication networks. Semiconductor lasers are so-called Class B lasers, in which the polarization of the electric field can be adiabatically eliminated. As a consequence, they can be described well by three-dimensional rate equations, one for the complex electric field E(t) and one for the population inversion N (t) (the number of excited states that can produce a single photon). It turns out that the phase φ(t) of the electric field follows the two equations for the optical intensity P (t) = |E(t)| 2 and the inversion N (t). Therefore, a solitary semiconductor laser is essentially a two-dimensional dynamical system that cannot exhibit chaotic dynamics. The only observable dynamical behavior is a damped periodic exchange between the electric field and the inversion. These oscillations are referred to as relaxation oscillations in the laser literature (not to be confused with relaxation oscillations in slow-fast systems); see, for example, [26,41] for an introduction to the theory of semiconductor lasers.