  Observational studies of GHz peaked spectrum (GPS) sources contribute to the
understanding of the radiative properties and interstellar environment of host
galaxies. We present the results from the multi-frequency high-resolution VLBI
observations of a sample of nine GPS sources at 8, 15, and 43 GHz. All sources
show a core-jet structure. Four sources show relativistic jets with Doppler
boosting factors ranging from 2.0 to 5.0 and a jet viewing angle between
10{\deg} and 30{\deg}. The core brightness temperatures of the other five
sources are below the equipartition brightness temperature limit with their jet
viewing angles in the range of 13.6{\deg} degrees to 71.9{\deg}, which are
systematically larger than those of relativistic jets in this sample. The
sources show diverse variability properties, with variability levels ranging
from 0.11 to 0.56. The measured turnover frequency in the radio spectrum ranges
from 6.2 and 31.8 GHz. We estimate the equipartition magnetic field strength to
be between 9 and 48 mG. These results strongly support the notion that these
GPS sources are young radio sources in the very early stage of their evolution.
