Erbium-doped aluminum oxide integrated optical amplifiers were fabricated on silicon substrates, and their characteristics were investigated for Er concentrations ranging from $0.27\text{to}4.2\times {10}^{20}{\mathrm{cm}}^{-3}$ . Background losses below $0.3\mathrm{dB}∕\mathrm{cm}$ at $1320\mathrm{nm}$ were measured. For optimum Er concentrations in the range of $1\text{to}2\times {10}^{20}{\mathrm{cm}}^{-3}$ , an internal net gain was obtained over a wavelength range of $80\mathrm{nm}$ $(1500–1580\mathrm{nm})$ , and a peak gain of $2.0\mathrm{dB}∕\mathrm{cm}$ was measured at $1533\mathrm{nm}$ . The broadband and high peak gain are attributed to an optimized fabrication process, improved waveguide design, and pumping at $977\mathrm{nm}$ as opposed to $1480\mathrm{nm}$ . In a $5.4\text{-}\mathrm{cm}$ -long amplifier, a total internal net gain of up to $9.3\mathrm{dB}$ was measured. By use of a rate-equation model, an internal net gain of $33\mathrm{dB}$ at the $1533\mathrm{nm}$ gain peak and more than $20\mathrm{dB}$ for all wavelengths within the telecom C-band $(1525–1565\mathrm{nm})$ are predicted for a launched signal power of $1\mu \mathrm{W}$ when launching $100\mathrm{mW}$ of pump power into a $24\text{-}\mathrm{cm}$ -long amplifier. The high optical gain demonstrates that ${\mathrm{Al}}_2{\mathrm{O}}_3:{\mathrm{Er}}^{3+}$ is a competitive technology for active integrated optics.