The 1:1 adduct of dimethyl zinc with triethylamine is an attractive precursor for the growth, using metal organic vapor phase epitaxy (MOVPE), of zinc based II‐VI compounds due to its high purity and suppression of unwanted pre‐reactions. A key parameter in MOVPE is the vapor pressure of the precursors which needs to be known in order to control the correct concentrations of organometallics entering the reactor. The literature on the vapor pressure of this precursor has been based on static measurements and has been inconsistent with the observed growth rates for ZnTe and ZnSe. An Epison ultrasonic monitor has been used to measure the concentrations under dynamic conditions and predict saturated vapor pressure (log10p=9.80–2596/T) which agree closely with the growth rate measurements but are up to a factor of 10 smaller than the static measurements. The reasons for these discrepancies are discussed. ©1996 American Institute of Physics.