A strip/slot hybrid arsenic tri-sulfide waveguide with a horizontal silicon dioxide slot is proposed. The waveguide exhibits an ultra-flat and low dispersion profile with four zero-dispersion wavelengths. Tuning structural parameters of the waveguide causes tailoring the dispersion. There is only a low dispersion of approximately ± 3 ps/(nm · km) over a 1035 nm bandwidth. It is shown that the waveguide has less sensitivity to the variations of the structural parameters and fabrication errors compared to silicon waveguides. Moreover, nonlinear coefficient, figure of merit, third-order dispersion and phase-matching condition in four-wave mixing are studied. This waveguide has a great potential for nonlinear applications in a wide range of wavelengths.