We describe our measurements of linewidths of the twoJ=2‐1 transitions (232.24 and 236.25 A˚) and theJ=0‐1 transition (196.20 A˚) of Ne‐like germanium soft x‐ray laser in slab targets. The high resolution spectral measurement was performed using a grazing incidence spectrometer with an x‐ray CCD camera. Time integrated linewidths, the full width at half maximum, of the twoJ=2‐1 lasing lines are about 20(±4) mA˚ when the gain‐length product (GL) is ∼8. The linewidth of theJ=0‐1 line is measured to be 25 mA˚ as the GL is ∼5. The measured linewidths of the 236.25 A˚ line are slightly narrower than those of 232.24 A˚ in the same shot, reflecting their different intrinsic linewidths. For theJ=2‐1 transitions, the thermal Doppler broadening (43 mA˚ inhomogeneous) has been obtained by one‐dimensional hydrodynamic simulation of the plasma expansion, and the collisional broadening (15 mA˚ homogeneous) has been considered with all inelastic electron collisional rates among the transition levels in the plasma. The predicted 52 mA˚ Voigt profile intrinsic linewidth for the 236.25 A˚ line has been used to calculate linewidth narrowing by the one‐dimensional model of amplified spontaneous emission. The experimental data are in agreement with the model calculation in the short targets. Spectral narrowing is not evident in the long targets. We examined soft x‐ray propagation in the plasma by ray‐trace calculation. It is shown that refraction is an important factor affecting the spectral narrowing of soft x‐ray lasers. ©1995 American Institute of Physics.