Thai technicians usually arrive in Vietnam not under individual employment contracts but inside a technical services agreement between the Thai parent and the Vietnamese plant: line commissioning, worker training, periodic maintenance. That structure creates a two-layer question many companies answer wrongly from the outset: is the money paid to the Thai side the technicians’ personal income (subject to personal income tax) or the Thai company’s service revenue (subject to foreign contractor tax) — and are the technicians themselves exempt in Vietnam under the treaty? This article analyses Thai experts; other ASEAN nationalities in the series, such as Malaysia and the Philippines, have similar treaty architecture but different secondment structures.
1. The individual layer: residence under Law 109/2025/QH15
Where a Thai technician is treated as an individual working in Vietnam, his residence follows Article 2 of PIT Law 109/2025/QH15: presence of 183 days or more in a calendar year or in 12 consecutive months from first arrival, or a regular place of abode in Vietnam under a fixed-term home lease, makes him a resident — worldwide income on the five-bracket scale in Article 9, with Article 10 relief (VND 15.5 million monthly for the taxpayer and VND 6.2 million for each dependant). Below the threshold, the individual pays 20% on Vietnam-source income. The distinctive feature of service technicians is interrupted presence across maintenance visits, so the count must run on the rolling 12-month window, and the “Vietnam income” element must be carved out of the total service contract value on a defensible basis — an unsupported carve-out is the single largest dispute source.
2. The treaty layer: Article 15 and the borne-by condition
The Vietnam–Thailand double taxation agreement is in force; its dependent personal services article (Article 15) taxes a Thai resident’s salary only in Thailand if presence in Vietnam does not exceed 183 days in the relevant 12-month period, the payer is not a Vietnamese resident, and the salary is not borne by a permanent establishment in Vietnam. In the service-contract model, the third condition is the permanent fracture point: if the Vietnamese plant bears the technicians’ personnel cost — even indirectly through a service price computed per head or per man-day — the authority may conclude the salary is borne in Vietnam, and the individual taxing right belongs to Vietnam. A service contract structure does not automatically “shield” personal income; it holds only where the service price is a lump sum for work results and the Thai company genuinely is the employer bearing risk and directing the technicians.
3. Coordination with foreign contractor tax
One technical services contract can generate two different obligations at once: foreign contractor tax on the Thai company’s service revenue in Vietnam, and personal income tax for each technician if the treaty conditions fail. The Vietnamese company, as withholding agent, must run both layers in one file: the service contract and result-based acceptance records; the technician list, work calendars and entry–exit stamps; individual tax residence certificates from the Thai Revenue Department when the treaty is claimed at the individual layer; and a labour-cost breakdown of the service price where one exists. The classic error is handling only the contractor-tax layer and assuming the individual layer is thereby settled — on audit, the authority separates each individual and assesses the personal income tax never withheld.
4. Risks and structuring recommendations
Three risks repeat in the Thai group: carving the salary element out of the service price by feel, without a market basis; technicians staying across many maintenance rounds until cumulative days breach the treaty window; and individual residence certificates never prepared because the company assumed only the Thai company’s papers were needed. The practical recommendation is to decide the structure when the service contract is signed: lump-sum-by-result or per-man-day pricing; who is the real employer; and if technicians may stay long, switching to Vietnamese personal income tax withholding from the start instead of resting a treaty exemption on a thin file.
This article has been quality-reviewed by the FLAW AI Legal Council