At ultrahigh levels of pulsed current pumping, the characteristics of semiconductor lasers based on an asymmetric heterostructure with a broadened lateral waveguide of a mesa-stripe design are studied. A peak power of 5.1 W is demonstrated at a pump current amplitude of 10 A. Three types of spatial dynamics of laser radiation are determined: the first one is a slow (~ 200 ns) intensity profile variation along the lateral near field at initial level of pump currents; the second one is a presence of fast (~ 10 ns) processes of mode competition at moderate pump currents; the third one is a chaotic temporal behavior of the output power at maximum pump currents.