The major upgrade of the Inner Tracking System (ITS) of the ALICE detector is being carried out to meet the challenges of the physics program of the ALICE experiment after the LHC Long Shutdown 2.The strategy of the ALICE ITS upgrade is based on the application of Monolithic Active Pixel Sensors (MAPS) developed by the ALICE collaboration using 0.18$~$$\mu$m TowerJazz technology. These sensors form seven concentric layers resulting in an overall detection area of 10$~$m$^2$. The layers of the upgraded ITS are split into the Inner and Outer Barrels.
Currently, the ITS modernization is entering its terminal phase, which means finalization of the production and construction together with the beginning of the on-surface commissioning.
The on-surface commisioning activity is meant to obtain a comprehensive view of the detector performance before installation inside the cavern. It includes the quality control of the main systems and components, namely the tests of the Inner and Outer Barrels, Electronics, Power System, Cooling System as well as detector calibration. Commissioning shifts are ongoing for the detector monitoring running for 24 hours per day. The shift crew is carrying out particularly threshold tests, tests of the noise performance and monitors the key parameters of voltages, currents and temperatures. For the assembled layers cosmic muon data are already being gathered.
The status of the ongoing assembly will be presented together with the first results of the detector performance obtained during the commissioning.