${\mathrm{K}}^{+}–{\mathrm{Na}}^{+}$ ion-exchanged channel waveguide amplifiers have been fabricated in ${\mathrm{Er}}^{3+}∕{\mathrm{Yb}}^{3+}$ codoped acid-resistant aluminum germanate (NMAG) glasses. The Judd–Ofelt parameters indicate high asymmetry and strong covalent environment in the glass substrates. The optical gain and the relative gain (the signal enhancement) of a $2.5\mathrm{cm}$ long waveguide amplifier were measured to be 9.10 and $8.16\mathrm{dB}$ , respectively, and after compensating both the propagation loss and the absorption loss, a maximum internal gain of $\sim 2.0\mathrm{dB}$ at $1.534\mu \mathrm{m}$ was obtained, which reveals the successful employment of the thermal ion-exchange technology on the low phonon energy glasses. Based on this work, ion-exchanged ${\mathrm{Pr}}^{3+}$ , ${\mathrm{Tm}}^{3+}$ , and ${\mathrm{Ho}}^{3+}$ doped NMAG glass waveguides will bring surprises in developing O-, S- and U-band waveguide amplifiers, infrared UV-writing grating waveguide lasers, and compact integrated optical devices.