We report experimental work on the terahertz emission characteristics of InAs/GaAs quantum dot (QD) structures and GaAs/AlGaAs modulation-doped heterojunctions (MDH’s), excited by femtosecond laser. Results showed that the terahertz emission from MDH’s can provide information on the GaAs/AlGaAs interface quality while the QD structures have the potential for being intense terahertz emitters; rivaling the emission intensity of p-type bulk InAs.