On the basis of summation of previous electron transit time relations for the cylindrical microelectronics device, calculated mathematically the typical value of the electron transit time at the Terahertz region for cylindrical vacuum microelectronics diode, by using of the method of an equivalent diode, approximately calculated a typical value of the electron transit time at the Terahertz region for cylindrical vacuum microelectronics triode too. The application possibility for the cylindrical vacuum microelectronics device at the Terahertz region has been estimated from the point of electron transit time.